, either for the musicians who play it, or, when the going gets rough, for the listeners who find themselves within earshot. Sometimes you wonder how the instrument found its way from the hunting lodge to the orchestra.

At the Mostly Mozart Festival in recent weeks, the intractable early version of the horn has made its way into the Rose Theater as a series of period-instrument bands from Germany, England and Italy performed music ranging from Italian Baroque choral works to Mozart opera. When these groups were at their best, a listener whose fondness for period instruments dates to the 1960s could reflect on how far the performance standard has risen since.

In those days period ensembles that sounded vigorous on disc often proved anemic in concert, and the instruments’ antique technology was regularly blamed for mediocre performances. Nowadays, the performances are more typically extroverted and expressive, and although period instruments, by definition, have not been modernized to make them easier to play, listeners are no longer asked to consider their difficulty when a performance goes awry.

Except, that is, when the horn notes crack and slither. The horn remains the wild card in period-instrument orchestras, and in modern ones too. And if you find yourself cringing when horn players falter badly — as I did on Aug. 5, when Concerto Italiano played three Vivaldi concertos with prominent horn parts — caveats about the instrument’s intransigence come quickly to mind.

It’s worth understanding the challenges hornists face. In its 17th- and 18th-century form, the horn is basically just a long, flared pipe wound into two or three coils, with a mouthpiece on the end. What it lacks, compared with today’s horn, is the valve mechanism: the complex tubing and finger keys at the center of a modern horn that let hornists play chromatically and in different keys.

Without recourse to valves, hornists are most at home in the relatively few notes in the overtone series that come naturally to a bit of coiled metal: mainly, the notes you hear in hunting and military calls. As the music grows more complex, the technical demands escalate. One resource hornists have is hand-stopping: by putting a hand inside the instrument’s bell, they can flatten the pitch to produce chromatic notes.

When everything goes right, hornists can work miracles. You need only have heard James Sommerville, the Boston Symphony’s principal hornist, play Elliott Carter’s Horn Concerto at Tanglewood a few weeks ago to know how chromatic (and lyrical) a horn line can be. But you can see the potential for pitch problems. And a bit of condensation from a player’s breath adhering to the inside of a coil can lead to cracked notes, or “clams.”

As is often the case, when Concerto Italiano’s hornists were good, they were great. Their sound had a fascinatingly gritty texture, much closer to the horn’s hunting-party origins than to the mellow, warm sound of a modern instrument. But when they were off — oh, dear, what a mess!

Strangely, some believe that period horn playing is meant to sound thus. When I was in music school, I had a job in a record store and would sometimes stay after hours to listen to new releases. One was a period-instrument recording of Handel’s “Water Music” on which the horns were consistently flat. When I crinkled my nose, the store’s manager said, dismissively:

“Oh, you don’t understand. It’s only because of showoffs like Don Smithers” — a brilliant Baroque trumpeter who was also my music history teacher at the time — “that people think these instruments can be played in tune. But they aren’t meant to be.”

I didn’t buy that argument then, and having heard many superb Baroque hornists, I find it less tenable now.

For some reason — maybe it’s a little-documented, mouth-drying effect of global warming — the last season was particularly rough for hornists. In a concert of Brahms and Schumann works at the 92nd Street Y in December, the usually reliable David Jolley became ensnared in every tangle a hornist can encounter (or create), including serious balance issues in ensemble pieces. And visiting orchestras seemed more prone than usual to horn flaws.

But surely the most catastrophic horn performance of the season — of many seasons, for that matter — was at the New York Philharmonic in March, when Alan Gilbert, conducting his first concert with the orchestra since having been appointed its next music director, opened his program with Haydn’s Symphony No. 48, a work with two prominent and perilous horn parts.

The Philharmonic has long been action central for horn troubles; its principal player, Philip Myers, is wildly inconsistent, and the rest of the section is also accident-prone. Much of the time Mr. Myers’s playing is squarely on pitch, shapely and warm, and when it is, it’s everything you want in a French horn line. But he cracks, misses or slides into pitches often enough that when the Philharmonic plays a work with a prominent horn line, you brace yourself and wonder if he’ll make it.

The Haydn symphony was a real clambake.

Mentioning hornists’ failings in reviews invariably brings plenty of e-mail messages, often from people who did not hear the performances but feel moved to defend a player’s reputation. Perhaps not surprisingly, most of these correspondents have variations on the word horn (“corno” or “horncall,” for example) in their e-mail addresses, and they usually identify themselves as hornists, as if their addresses didn’t make that clear.

In the case of the Haydn, some offered amazing conspiracy theories. The most interesting was that Mr. Gilbert had programmed the work knowing that it would be botched, so that he would later have reason to replace Mr. Myers. (Mr. Gilbert doesn’t seem that Machiavellian.) Another blamed the orchestra’s management for allowing Mr. Gilbert to program it.

Still others offered technical excuses: that the work requires a variety of horn that Mr. Myers doesn’t play, for instance. (That an orchestra’s programming is announced months in advance — ample time to deal with such technical problems or lobby to have the work replaced — seems not to have troubled anyone.)

Of about a dozen e-mail messages, all but one correspondent found someone other than the players to blame for the performance. A few blamed me: I am supposedly a raging cornophobe with some deep-seated resentment of horns and hornists.

To the contrary. I played the horn briefly as a teenager, somewhere between the violin and the trombone (which had a nicer bite), and I gave up brass instruments only when I realized that continuing would mean spending weekends marching around at football games in a dopey band uniform. It was the late 1960s; that kind of thing just wasn’t done.

Nearly a decade later, as a composition student, I revisited the instrument and what it could (ideally) do when I wrote an unaccompanied horn piece and a quartet for horn, violin, bassoon and percussion (what was I thinking?) for a hornist friend.

I like the horn, honest. And I know how difficult it is to get a good, centered, well-tuned sound out of it.

But here’s the thing about musical performance: It’s all difficult. It’s meant to be. Composers write, and have always written, music that pushes the limits of technique. And if you’re onstage in a professional capacity, you’re expected to be able to negotiate it. That’s the least audiences expect, and it’s a precondition for what they buy tickets for: to be moved by an interpretation; to savor its nuances and to hear something revelatory, whether the work is new or familiar.

If, instead, they end up wincing at mistuned notes and reminding themselves how tough the instruments are, they’ve been pushed out of the zone. And at that point, no amount of rationalization will make the performance anything but a sow’s ear.